Just in case anybody out there was wondering. Here's the reply I received from Sirius.
Can't believe I had a reply. This really does look like this site is every growers dream.
Hello,
We use perlite because it's super airy (much more than clay pebbles by volume), it helps with drainage, it's available everywhere and it's cheap. I know that coco/pebbles will work, but I think you'd probably get better results using a mixture of coco/perlite if only because the roots will have a better environment. Good luck and happy growing!
Sirius
GrowWeedEasy.com